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Chemically characterizing the cortical cell nano-structure of human hair using atomic force microscopy integrated with infrared spectroscopy (AFM-IR).

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cam.issuedOnline2021-12-14
dc.contributor.authorFellows, AP
dc.contributor.authorCasford, MTL
dc.contributor.authorDavies, PB
dc.contributor.orcidFellows, AP [0000-0002-5885-8144]
dc.date.accessioned2022-01-05T10:45:42Z
dc.date.available2022-01-05T10:45:42Z
dc.date.issued2022-02
dc.date.submitted2021-09-16
dc.date.updated2022-01-05T10:45:42Z
dc.description.abstractOBJECTIVE: The use of conventional microscopy and vibrational spectroscopy in the optical region to investigate the chemical nature of hair fibres on a nanometre scale is frustrated by the diffraction limit of light, prohibiting the spectral elucidation of nanoscale sub-structures that contribute to the bulk properties of hair. The aim of this work was to overcome this limitation and gain unprecedented chemical resolution of cortical cell nano-structure of hair. METHODS: The hybrid technique of AFM-IR, combining atomic force microscopy with an IR laser, circumvents the diffraction limit of light and achieves nanoscale chemical resolution down to the AFM tip radius. In this work, AFM-IR was employed on ultra-thin microtomed cross-sections of human hair fibres to spectrally distinguish and characterize the specific protein structures and environments within the nanoscale components of cortical cells. RESULTS: At first, a topographical and chemical distinction between the macrofibrils and the surrounding intermacrofibillar matrix was achieved based on 2.5 × 2.5 μm maps of cortical cell cross-sections. It was found that the intermacrofibrillar matrix has a large protein content and specific cysteine-related residues, whereas the macrofibrils showed bigger contributions from aliphatic amino acid residues and acidic-/ester-containing species (e.g. lipids). Localized spectra recorded at a spatial resolution of the order of the AFM tip radius enabled the chemical composition of each region to be determined following deconvolution of the Amide-I and Amide-II bands. This provided specific evidence for a greater proportion of α-helices in the macrofibrils and correspondingly larger contributions of β-sheet secondary structures in the intermacrofibrillar matrix, as inferred in earlier studies. Analysis of the parallel and antiparallel β-sheet structures, and of selected dominant amino acid residues, yielded further novel composition and conformation results for both regions. CONCLUSION: In this work, we overcome the diffraction limit of light using atomic force microscopy integrated with IR laser spectroscopy (AFM-IR) to characterize sub-micron features of the hair cortex at ultra-high spatial resolution. The resulting spectral analysis shows clear distinctions in the Amide bands in the macrofibrils and surrounding intermacrofibrillar matrix, yielding novel insight into the molecular structure and intermolecular stabilization interactions of the constituent proteins within each cortical component.
dc.description.sponsorshipEPSRC and Unilever on Grant EP/R511870/1
dc.identifier.doi10.17863/CAM.79431
dc.identifier.eissn1468-2494
dc.identifier.issn0142-5463
dc.identifier.otherics12753
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/331983
dc.languageen
dc.language.isoeng
dc.publisherWiley
dc.publisher.urlhttp://dx.doi.org/10.1111/ics.12753
dc.subjectAmide Deconvolution
dc.subjectAtomic Force Microscopy
dc.subjectInfrared Nanospectroscopy (AFM-IR)
dc.subjectcortical cells
dc.subjecthair
dc.subjectprotein secondary structures
dc.subjectHair
dc.subjectHumans
dc.subjectMicroscopy, Atomic Force
dc.subjectProtein Structure, Secondary
dc.subjectProteins
dc.subjectSpectrophotometry, Infrared
dc.titleChemically characterizing the cortical cell nano-structure of human hair using atomic force microscopy integrated with infrared spectroscopy (AFM-IR).
dc.typeArticle
dcterms.dateAccepted2021-11-18
prism.publicationNameInt J Cosmet Sci
pubs.funder-project-idEPSRC (2110577)
pubs.funder-project-idEngineering and Physical Sciences Research Council (EP/R511870/1)
rioxxterms.licenseref.urihttp://creativecommons.org/licenses/by/4.0/
rioxxterms.versionVoR
rioxxterms.versionofrecord10.1111/ics.12753

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